A Crystal-Less BLE Transmitter With Clock Recovery From GFSK-Modulated BLE Packets

In this article, we present a crystal-less Bluetooth low-energy (BLE) transmitter using RF reference recovery directly from GFSK-modulated BLE packets. In order to achieve fast frequency calibration from modulated signals and reduce interference from other BLE users, the transceiver consists of a back-channel wake-up receiver, a clock-recovery receiver, a transmitter, and a dual-all-digital phase-locked loop (ADPLL) frequency synthesizer for system wake-up, clock-recovery, packet transmission, and frequency calibration. An embedded averaging processing unit in the loop filter of the ADPLL is proposed to retrieve accurate frequency information from GFSK-modulated signals. A prototype chip is fabricated in 40-nm CMOS for verification. The crystal-less transmitter with clock recovery meets all BLE requirements for SIR, making this a robust solution for removing the crystal even in densely populated networks.